feat: add support for user-provided OCR model

The ocr_model field added to the OcrOptions class with a reference
 to the BaseOcrModel inheritor class.
In case the options are not one of supported model options,
 the class from this field is used.

Signed-off-by: vdaleke <vdalekesmirnov@gmail.com>

docling/datamodel/pipeline_options.py

@@ -2,11 +2,13 @@ import logging
 import os
 from enum import Enum
 from pathlib import Path
-from typing import Annotated, Any, Dict, List, Literal, Optional, Union
+from typing import Annotated, Any, Dict, List, Literal, Optional, Type, Union
 
 from pydantic import AnyUrl, BaseModel, ConfigDict, Field, model_validator
 from pydantic_settings import BaseSettings, SettingsConfigDict
 
+from docling.models.base_ocr_model import BaseOcrModel
+
 _log = logging.getLogger(__name__)
 
 
@@ -85,6 +87,7 @@ class OcrOptions(BaseModel):
     bitmap_area_threshold: float = (
         0.05  # percentage of the area for a bitmap to processed with OCR
     )
+    ocr_model: Optional[Type[BaseOcrModel]] = None
 
 
 class RapidOcrOptions(OcrOptions):
@@ -151,6 +154,7 @@ class TesseractCliOcrOptions(OcrOptions):
 
     kind: Literal["tesseract"] = "tesseract"
     lang: List[str] = ["fra", "deu", "spa", "eng"]
+
     tesseract_cmd: str = "tesseract"
     path: Optional[str] = None
 
@@ -164,6 +168,7 @@ class TesseractOcrOptions(OcrOptions):
 
     kind: Literal["tesserocr"] = "tesserocr"
     lang: List[str] = ["fra", "deu", "spa", "eng"]
+
     path: Optional[str] = None
 
     model_config = ConfigDict(
@@ -176,6 +181,7 @@ class OcrMacOptions(OcrOptions):
 
     kind: Literal["ocrmac"] = "ocrmac"
     lang: List[str] = ["fr-FR", "de-DE", "es-ES", "en-US"]
+
     recognition: str = "accurate"
     framework: str = "vision"
 
@@ -271,13 +277,7 @@ class PdfPipelineOptions(PipelineOptions):
     do_picture_description: bool = False  # True: run describe pictures in documents
 
     table_structure_options: TableStructureOptions = TableStructureOptions()
-    ocr_options: Union[
+    ocr_options: OcrOptions = EasyOcrOptions()
-        EasyOcrOptions,
-        TesseractCliOcrOptions,
-        TesseractOcrOptions,
-        OcrMacOptions,
-        RapidOcrOptions,
-    ] = Field(EasyOcrOptions(), discriminator="kind")
     picture_description_options: Annotated[
         Union[PictureDescriptionApiOptions, PictureDescriptionVlmOptions],
         Field(discriminator="kind"),

docling/pipeline/standard_pdf_pipeline.py

@@ -13,6 +13,7 @@ from docling.datamodel.document import ConversionResult
 from docling.datamodel.pipeline_options import (
     EasyOcrOptions,
     OcrMacOptions,
+    OcrOptions,
     PdfPipelineOptions,
     PictureDescriptionApiOptions,
     PictureDescriptionVlmOptions,
@@ -73,6 +74,7 @@ class StandardPdfPipeline(PaginatedPipeline):
         if (ocr_model := self.get_ocr_model(artifacts_path=artifacts_path)) is None:
             raise RuntimeError(
                 f"The specified OCR kind is not supported: {pipeline_options.ocr_options.kind}."
+                " You can provide a custom OCR model class in the options."
             )
 
         self.build_pipe = [
@@ -190,6 +192,12 @@ class StandardPdfPipeline(PaginatedPipeline):
                 enabled=self.pipeline_options.do_ocr,
                 options=self.pipeline_options.ocr_options,
             )
+        elif isinstance(self.pipeline_options.ocr_options, OcrOptions):
+            if self.pipeline_options.ocr_options.ocr_model is not None:
+                return self.pipeline_options.ocr_options.ocr_model(
+                    enabled=self.pipeline_options.do_ocr,
+                    options=self.pipeline_options.ocr_options,
+                )
         return None
 
     def get_picture_description_model(